1. Field of the Invention
The present invention relates to a nozzle device for discharging molten metal, and more specifically to a nozzle device having an improved member supporting a nozzle.
2. Description of the Related Art
FIG. 4 shows a conventional nozzle device for discharging molten metal (prior art 1). Nozzle 1 has right-angled step portion 2 on the outer periphery of its upper end portion. Metal holder 3, which has a right-angled inner surface, is mounted on step portion 2. Nozzle 1 also has through hole 4 extending in the axial direction, for discharging molten metal.
FIG. 5 shows another conventional nozzle device for discharging molten metal (prior art 2). Nozzle 5 has tapered portion 6 on the outer periphery of its upper end portion. The outer diameter of tapered portion 6 gradually decreases toward the lower end. Metal holder 7 is mounted on the upper end portion of nozzle including tapered portion 6.
However, the conventional nozzle devices thus arranged have the following drawbacks:
(1) Prior art 1
Since stress is likely to concentrate on the holder 3 and is applied to step portion 2, the neck portion of nozzle 1 tends to break.
(2) Prior art 2
Since stress does not concentrate on holder 7, due to the presence of tapered portion 6, the neck portion of nozzle 5 is less likely to break than in the case of prior art 1. However, during the time the nozzle device is in use, holder 7 expands diametically, because of the heat of the molten metal flowing through it. As a result, nozzle 5 slips down from the holder. If nozzle 5 has slipped down a considerable extent by the time holder 7 begins to contract during a ladle exchanging operation or cooling operation, it will then be held tightly by holder 7, resulting in shearing stress being generated by the compressive force, and causing nozzle 5 to crack.